This invention relates to compositions which are useful as polymeric additive systems. This invention also relates to processes for making polymeric additive systems. This invention further relates to polymeric compositions that include a polymeric component and one or more polymeric additive system. This invention even further relates to processes for preparing polymeric compositions that include a polymeric component and one or more polymeric additive systems.
Numerous molded articles and films are manufactured from one or more of a variety of polymeric resins. Often times, these resins, by themselves, do not possess all of the properties required by the end use for which they are made. To overcome their shortcomings, these resins are generally blended with other components which exhibit the desired properties. Such components are typically known in the industry as polymeric additive systems.
Although polymeric additives can be made by a number of different ways, many are made by emulsion polymerization. Thereafter, the emulsion is dried to form a powder. The powder is then blended with the polymeric resin system whose properties need to be enhanced.
Accordingly, since many polymeric additives are blended with the polymeric resin when the additive is in a powder form, one significant limitation upon the development and/or selection of new polymeric additives is their ability to form a stable powder. The term “stable” as it pertains to powders means, among other things, the ability of the particles making up the powder to remain a flowable form during normal storage, handling and processing procedures. One reason for the existence of this problem is that many polymeric additives are relatively soft. Accordingly, they often have the tendency to stick together; thus, reducing the additive's stability. This phenomenon is often seen in polymeric additives designed to enhance the impact modification of the polymeric resin system since, in order to impart this property, the additive generally needs to be soft and/or rubbery.
One means of addressing this problem has been to use multi-layered polymeric additive systems. Such systems are typically known in the industry as a “core/shell” system. In most core/shell systems, the inner stage (i.e., the core) is relatively soft and/or rubbery; and the outer-stage (i.e., the shell) is relatively hard. The hardness of the outer shell keeps the particles from sticking together.
While the use of a core/shell system does remove one of the inherent problems associated with powdery polymeric additive systems, such powdery systems are still fraught with other problems. For example, powders are inherently dusty thereby making handling difficult. Powders also require that the additive contain a “hard” component, such as a hard shell polymer for effecting isolation; such a hard component in impact modifiers often does not contribute to the effectiveness of a particular impact modifier. Powders also tend to “compact” under the stress of heat, moisture, and/or weight, causing clumping and poor flowability.
Notwithstanding the aforementioned problems associated with powdery plastic additive systems, they are still the additive system of choice. However, the industry continues to look for alternatives to such systems. One of the alternatives that has been suggested is disclosed in U.S. Pat. No. 3,864,432. The polymeric additive system disclosed in this Patent has a solid component that does not exceed 50 weight percent of the additive system's total weight. While such a system can be used, there are many advantages associated with systems that have a higher solids concentration. For example, some of the advantages associated with using an additive system that has a solids concentration greater than 50 weight percent “high solids” includes increasing the overall concentration, and thereby effectiveness and efficiency of the additives. Another advantage is that a high solids additive will require less liquid; because the liquid may contain volatile components (e.g. water) which must be removed during processing with polymeric resins, high solids additive systems will have increased process efficiency.
Many other plastics additives are commonly used in the plastics industry to modify the processability and/or properties of polymeric resins. Examples of these other plastics additives include: waxes; pigments; opacifiers; fillers; exfoliated clays; toners; antistatic agents; metals; flame retardants; thermal stabilizers; co-stabilizers; antioxidants; cellulosic materials; internal lubricants; external lubricants; oils; rheology modifiers; powder flow aids; melt-flow aids; dispersing aids; UV stabilizers; plasticizers; fillers; optical modifiers; surface roughness modifiers; surface chemistry modifiers; adhesion modifiers; surface hardeners; compatibilizers; diffusion barrier modifiers; stiffeners; flexibilizers; mold release agents; processing modifiers; blowing agents; thermal insulators; thermal conductors; electronic insulators; electronic conductors; biodegradation agents; antistatic agents; internal release agents; coupling agents; flame retardants; smoke-suppressers; anti-drip agents; colorants, and the like, and/or combinations thereof.
As seen by the examples set out above, many polymeric additives come in a variety of physical forms such as volatile liquids, sticky liquids, viscous liquids, pasty waxes, dusty powders, hard solids, and the like. Accordingly, they are often handled separately when formulating a polymeric composition containing the same. This creates obvious problems, especially when some of the additives which need to be added come in a liquid form, while others that are needed come in a powder form. Other inherent problems with the conventional ways of enhancing the properties of a polymeric composition through the use of a polymeric additive system include problems associated with handling a variety of additives include incompatibility with other additives or matrix, special processing or feeding requirements to incorporate uniformly or achieve desired dispersion behavior, morphology or final properties. Other problems associated with handling a variety of additives include incompatibility with other additives or matrix, special processing or feeding requirements to incorporate uniformly or achieve desired dispersion behavior, morphology or final properties, adhesion to, or interaction with, materials of construction used as containers in the blending operations.
Notwithstanding the problems associated with conventional polymeric additive systems, they will almost always be necessary due to the inherent deficiencies of polymeric compositions. However, the industry is continually searching for improved polymeric additive systems which resolve at least some of the aforementioned problems.